Making sure the faces are flat (for paper model)
Thanks to comments from users @lemon and @m.ardito I can answer this myself now.

The distorted face fixing can be done in two steps:


Identify the distorted faces by activating the "mesh analysis" in the properties menu (N key), select type: distortion.
Flatten the distorted faces by selecting them (Edit mode, face select mode) and then going to Mesh menu > Clean up > Make planar faces.